Rotary Drum of an Axial Compressor Having a Composite Web

ABSTRACT

A rotary drum of an axial compressor having a web made of composite material has an upstream flange for fastening the fan, a segment having a sealing flange upstream, a segment with a groove adapted to receive the bases of the vane of a first row of vanes, a segment with a groove adapted to receive the bases of the vane of a second row of vanes, and a segment with a groove adapted to receive the bases of the vane of a third row of vanes. These segments are made of metallic material mostly for reasons of mechanical resistance to the centrifugal forces. The segments are connected to each other with web segments made of composite material. The ends of the metallic segments have a dovetail-shaped section in a longitudinal plane that is able to ensure a positive connection with the composite material.

This application claims priority under 35 U.S.C. §119 to European Patent Application No. 09065612.4, filed 16 Jul. 2009, titled “Rotary Drum of an Axial Compressor Having a Composite Web,” which is incorporated herein by reference for all purposes.

BACKGROUND

1. Field of the Application

The application relates to a rotary drum of an axial turbomachine, more particularly to a drum of an axial compressor.

2. Description of Related Art

A compressor of an axial turbomachine conventionally comprises several compression stages, and therefore several rows of vanes, these rows being axially spaced apart from one another in order to arrange for annular spaces for the guide vane grids. The rotor conventionally comprises a drum and rows of vanes affixed to the drum. The drum thus has two main functions: to maintain the fixed vanes with respect to one another, and to set them in motion. To secure the vanes, an increased drum strength is required, particularly due to high centrifugal forces generated by the mass of the vanes and high rotation speeds when guiding the fluid stream more greatly requires a surface which is optimized from an aerodynamic standpoint and sealing means with the straightening stages.

Having several stages (typically 3 or 4) makes the drum quite long. Machining is thus made particularly difficult and costly, as shown in FIG. 1. FIG. 1 is a cross-sectional view showing a blank 1 made of a metallic material, conventionally titanium, adapted to be machined so as to make a finished drum. The drum has the general shape of an ogive and comprises three grooves 4, 6, and 8, adapted to receive three rows of vanes forming, with the vanes of the guide vane grid (not shown), three compression stages. The drum comprises an upstream flange in the area of the rotation and symmetry axis adapted to be fixed to an entry rotor blading, commonly referred to as “fan”. It comprises a sealing flange 3 adapted to cooperate with some “abradable” of the stator to prevent a leak upstream of the fluid stream displaced and compressed by the “fan”. It also comprises ribs, commonly referred to as knife edges, on both sides of each groove 4, 6, 8 of the row of vanes. These knife edges are adapted to cooperate in a tight manner, with the inner shrouds of the stators (not shown). A stiffener 9 is provided on the inner surface of the drum in the vicinity of the last groove 8. It must be noted that the general layout of the drum is such that a greater portion, typically on the order of 80%, of the material of the blank 1 must be removed by machining in order to achieve the drum 2 shown. Manufacturing the drum involves very high material and machining costs. Furthermore, machining in the concave portion of the drum is difficult due to its length and to the difficulty of accessing the inner surface of the drum.

Different constructions of rotary drums of axial turbomachines having several elements are known by one having ordinary skill in the art.

The document GB 1 272 200 discloses a drum made of several segments extending along the axis of rotation, whereby each segment comprises a recess adapted to receive a row of vanes and a section of web adjacent to the recess. These various segments are assembled and welded together in order to make a complete drum. The sections of the web are reinforced by applying fibers and an epoxy resin in a trough of their outer surfaces provided for this purpose. The purpose of these strips of composite material is to reinforce the drum with respect to the centrifugal forces, in particular those generated in the area of the rotor vanes. However, this design requires multiple operations such as applying the composite material, assembling the segments with each other and welding them, which means that the cost for making a drum still remains quite high.

The documents US 2007/0231144 and EP 1 406 019 A1 disclose similar teachings to those of the previous document.

The document U.S. Pat. No. 5,632,600 discloses a principle for building a rotor of an axial turbomachine whereby the rotor is constituted of a series of disks carrying the rows of vanes. The disks are assembled and fixed to one another by a mechanical connection such as putting into contact the corresponding teeth and by applying a strip of composite material to the mechanical connection. This substantial construction typical of a rotor with disks is not suitable for the construction of a drum such as described and shown in FIG. 1, particularly due to the thickness and shape of the strip of composite material.

Although great strides have been made in the area of rotary drums of axial compressors, many shortcomings remain.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an upper half of a known drum and of a blank made of a metallic material necessary to making it by machining said blank.

FIG. 2 is a cross-sectional view of an upper half of a drum in accordance with the present application, the drum being partially composite.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present application involves a rotary drum of an axial turbomachine, the drum comprising a wall, generally symmetrical, revolving about a longitudinal axis, said wall comprising, along said longitudinal axis: a first segment; a second segment; a third segment adjacent to the first and second segments and forming a web for connecting the first segment to the second segment; whereby the third segment is made of composite material and is connected to the first and/or second segment by molding said composite material onto an end of the first and/or second segment.

This construction has several advantages. Indeed, it makes it possible to make the segments to be machined from blanks such that they require less material to be removed in comparison with the machining of a drum made of one piece from a single blank. Moreover, fractioning the drum into segments diminishes the financial losses due to machining discards. Indeed, the fact of discarding one segment obviously makes for a much reduced financial loss than in the case where the entire drum is discarded. Machining metal segments is easier and therefore faster and less costly. The accessibility from the machining perspective provides a certain freedom when it comes to choosing the shape of a stiffener. The latter can be optimized from a functional point of view and not as a function of machining and of obtaining the blank. The composite material is used at the location where the stresses are the weakest, which results in a general optimization in terms of the weight while enjoying the advantages hereinabove mentioned. This construction also opens up new possibilities for repairing a drum.

According to an advantageous embodiment of the present application, the first and/or second segment is able to receive a row of vanes, preferably the first and/or second segment comprises a cavity in the form of a circular groove adapted to receive the bases of the vanes.

According to an advantageous embodiment of the present application, the cavity of the first segment has a section which diminishes toward the outside of the cavity so as to enable a fixation by mechanical embedding of the bases of the vanes.

According to another advantageous embodiment of the present application, the end of the first and/or second segment in contact with the composite material of the third segment has a shape adapted to facilitate the connection between the two segments.

According to an advantageous embodiment of the present application, the end of the first and/or second segment in contact with the composite material of the third segment has a section in a longitudinal plane in the form of a dovetail.

According to an advantageous embodiment of the present application, the third segment has a generally constant thickness between the connecting areas with the first and second segments.

According to an advantageous embodiment of the present application, the composite material of the third segment covers the end of the first and/or second segment on its outer surface and on its inner surface.

According to an advantageous embodiment of the present application, the third segment comprises at least one rib referred to as knife edge, on its outer surface, the knife edge being adapted to cooperate with a ring made of abradable material of a guide vane grid to ensure sealing.

According to an advantageous embodiment of the present application, the first and/or second segment is made of metallic material, preferably titanium.

The present application also involves a method of fabricating a rotary drum of an axial turbomachine, the drum comprising a generally symmetrical wall revolving about a longitudinal axis, the method comprising the following steps:

(a) preparing a first segment;

(b) preparing a second segment, distinct from the first segment;

(c) setting the first and the second segments in place; and

(d) fabricating a third segment made of composite material forming a connection web between the first segment and the second segment.

According to an advantageous embodiment of the present application, the method comprises the use of a device used for the steps (c) and (d).

According to an advantageous embodiment of the present application, the device comprises means for molding the third segment.

According to an advantageous embodiment of the present application, the device comprises means for counter-molding the third segment.

According to an advantageous embodiment of the present application, step (d) comprises applying the composite material onto an outer and/or inner surface of the end of the first and/or second segment.

According to an advantageous embodiment of the present application, step (d) comprises making a rib on the outer surface of the third segment adapted to cooperate with a ring made of an abradable material of a guide vane grid in order to provide sealing.

The drum 12 shown in FIG. 2 is the preferred embodiment of the present application. It is made of a series of metallic segments extending along the longitudinal axis which is also the rotation axis of the drum, these segments having generally mechanical properties and being connected to one another by web segments made of composite material.

The drum 12 has the general shape of an ogive. It comprises a fastening flange 20 at its upstream end. This flange is adapted to fasten the drum to the vaned disk, or “fan”, at the most upstream point of the compressor. The drum also comprises a segment 22 with an upstream sealing flange 13. The flange is adapted to cooperate in a sealing manner with a stationary element of the stator (not shown) in order to prevent a leak upstream of the fluid stream after the compression carried out by the “fan”. The drum also comprises three segments 24, 27, and 30, each comprising a groove or recess 14, 16, and 18, respectively, adapted to receive the bases of the vane. These different metal sections 20, 22, 24, 27, and 30 are connected to one another by web segments of the drum 21, 23, 26, and 29 made of composite material. This construction results in that the segments or sections of the drum subjected to greater mechanical stresses are conventionally made of metallic material and in that the segments or sections forming the web of the drum and being subjected to substantially weaker mechanical stresses are made of composite material.

The ends of the segments made of metallic material 20, 22, 24, 27, and 30 adapted to be connected to a segment made of composite material have a section in a longitudinal plane in the form of a dovetail in order to enable a positive-contact connection with the composite segment to which they are connected. The composite material covers the upper and lower surfaces of the dovetailed end.

The connection between the composite segments and the metallic segments shown in FIG. 2 is given only by way of example. Indeed, numerous alternatives are possible. The mechanical connection is typically ensured by cohesion between the composite material and the contact surface of the metallic material. Just as the example of connection shown in FIG. 2, the connection can also be reinforced by a retention shape of the metallic part, namely, able to ensure a positive contact with the composite material. An L-shape, hook shape, or any other shape section with a positive contact, for example, could be considered.

The material of the metallic segments is typically titanium, for reasons of weight. Other materials or variations known by one having ordinary skill in the art can, of course, be considered.

The composite material of the segments forming the web typically comprises reinforcement fibers and a resin forming a matrix and making the fibers cohesive. The fibers can be glass, carbon, aramid (Kevlar®), boron, silica, or high-modulus polyethylene fibers. They are applied in the form of uni- or multi-directional naps. The resin is typically a thermosetting resin of the unsaturated polyester, phenolic, epoxide, polyurethane, polyimide type, or other.

According to an embodiment of the present application, the assembly of the different segments in view of fabricating a finished drum comprises the use of a device (not shown) used for positioning the preformed segments with respect to one another in a precise manner. This device is also used as a mold for applying composite materials making up the connecting segments. For example, the device can comprise sections of an inner or outer mold on which the reinforcement naps are laid and the resin is manually applied (contact molding). Alternatively, the materials can be applied by simultaneously spraying up resin and fibers. Preferably, the device comprises a mold and a counter-mold, the reinforcement naps being arranged in the air gap of the mold. This makes it possible to inject liquid resin between the mold and the counter-mold through the reinforcement until the cavity is entirely filled up. After the resin has set, the mold is opened and the piece is taken out of the mold. Other methods known by one having ordinary skill in the art are possible, such as, for example, matched-die molding, or molding by compound injection (mass to be molded made of resin, various charges and adjuvants, reinforced by chopped strands).

The web segments 26 and 29 comprise knife edges 15 and 17, respectively, directly molded with the segments. The knife edges are thin circular ribs directed toward the outside of the drum. They are adapted to cooperate by friction in a sealing manner with the inner surface of a ring of friable material, commonly referred to as “abradable”, mounted on an inner shroud of a blade row, adapted to rectify the airflow which is compressed and accelerated by the rotation of a row of rotary vanes directly upstream.

It must be noted that these knife edges do not necessarily have to be molded in one piece with the web of the segment. Indeed, they can be made out of another material, more conventionally a metallic material, and then be embedded in the composite material.

The metallic segments, more particularly those subjected to great centrifugal forces, particularly due to the presence of the vanes, can be equipped on their inner surfaces with reinforcements 25, 28, and 31 machined or forged directly in the mass. Machining such reinforcements is made much easier and therefore less costly by the construction of the segment around the drum. The presence of these reinforcements can result in a gain of material which would otherwise be distributed over the thickness of the segment in order to provide a stiffness and a resistance equivalent to the centrifugal forces exerted.

It must be noted that all the web portions of the drum do not necessarily have to be made of composite material. Indeed, although the example in FIG. 2 shows a composite segment between each pair of neighboring segments adapted to be subjected to great forces, it is absolutely possible to provide composite segments only between certain segments and to leave one or several webs made of a conventional metallic material, as a function of various design parameters such as for example the manufacturing cost and the available machining capacities. The contrary is also applicable, which means that it is also possible to provide for making more elements of the drum from composite as a function of the feasibility in terms of mold and mechanical resistance forces.

A segment extending along the longitudinal axis of a rotary drum of an axial turbomachine is also disclosed, the drum comprising a generally symmetrical wall revolving about a longitudinal axis, the segment being adapted to receive a row of vanes and comprising an edge extending along the longitudinal axis whose section on a longitudinal plane has a shape, preferably dovetailed, which is adapted to enable a positive-contact connection extending along the longitudinal axis with an element made of composite material molded on said edge. The various alternatives described in the present application and in particular in relation to FIG. 2 apply only to the segment such as described hereinabove. 

1. A rotary drum of an axial turbomachine, comprising: a first segment; a second segment; and a third segment adjacent to the first segment and the second segment, the third segment forming a web for connecting the first segment to the second segment; wherein the first segment, the second segment, and the third segment form a generally symmetrical wall revolving about a longitudinal axis; and wherein the third segment is made of composite material and is connected to at least one of the first segment and the second segment by molding the composite material onto an end of at least one of the first and the second segment.
 2. The rotary drum according to claim 1, wherein at least one of the first segment and the second segment is adapted to receive a row of vanes.
 3. The rotary drum according to claim 1, wherein at least one of the first and the second segment comprises: a cavity in the form of a circular groove adapted to receive bases of the vanes.
 4. The rotary drum according to claim 3, wherein the cavity includes a section that is diminished toward the outside of the cavity, so as to enable a fixation by mechanically embedding the bases of vanes.
 5. The rotary drum according to claim 1, wherein the end of each segment in contact with the composite material of the third segment has a shape that facilitates the connection between such segment and the third segment.
 6. The rotary drum according to claim 1, wherein the end of each segment in contact with the composite material of the third segment has a section in a longitudinal plane in the form of a dovetail.
 7. The rotary drum according to claim 1, wherein the third segment has a generally constant thickness between the connecting areas with the first segment and the second segment.
 8. The rotary drum according to claim 1, wherein the composite material of the third segment covers both the outer surface and the inner surface of the end of each segment connected thereto.
 9. The rotary drum according claim 1, wherein the third segment comprises: at least one knife edge on an outer surface thereof, the knife edge being adapted to cooperate with a ring made of abradable material of a guide vane grid in order to ensure sealing.
 10. The rotary drum according to claim 1, wherein at least one of the first segment and the second segment is made of a metallic material.
 11. The rotary drum according to claim 10, wherein at least one of the first segment and the second segment is made of titanium.
 12. A method for manufacturing a rotary drum of an axial turbomachine, comprising: providing a first segment; providing a second segment, distinct from the first segment; setting the first segment and the second segment in place about a longitudinal axis; and providing a third segment made of composite material, the third segment forming a connection web between the first segment and the second segment.
 13. The method according to claim 12, comprising: using a device to set the first segment and the second segment in place and to form the connection web between the first segment, the second segment, and the third segment.
 14. The method according to claim 13, wherein the device comprises: a means for molding the third segment.
 15. The method according to claim 13, wherein the device comprises: a means for counter-molding the third segment.
 16. The method according to claim 12, wherein the forming a connection web between the first segment, the second segment, and the third segment comprises: applying a composite material on at least one of an outer surface and an inner surface of the end of at least one of the first segment and the second segment.
 17. The method according to claim 12, wherein the forming a connection web between the first segment, the second segment, and the third segment comprises: providing a rib on an outer surface of the third segment adapted to cooperate with a ring made of abradable material of a guide vane grid to ensure sealing. 